Succinic acid is widely used for a polymer, a food, a medicine, and a raw material for synthesis of other chemicals. Particularly, when it is used as a raw material for a polymer, succinic acid of high purity is required in order to maintain the degree of polymerization and prevent coloring. It is possible to obtain succinic acid of high purity by increasing the number of purification stages, but in order to perform the industrial production economically, it is necessary to simplify the steps of separation and purification.
Generally, in the production of succinic acid by a fermentation method, when the fermentation is carried out without a pH control, the produced succinic acid accumulates in the reaction system as the reaction progresses. Thereby, pH of the reaction solution is lowered and deviates from a suitable range for microorganisms to produce the succinic acid, and as a result, the rate of succinic acid production is greatly slowed. Therefore, the production rate is maintained by controlling the pH usually by adding an alkaline material. Thus, an alkali-metal succinate is a form commonly observed in the reaction solution for producing succinic acid by a fermentation method.
As a method for producing succinic acid of high purity from a reaction solution containing an alkali metal succinate, the method to change an unsaturated aqueous solution of the salt of succinic acid into a supersaturated aqueous solution of free succinic acid by a water-splitting electrodialysis followed by crystallization from the said supersaturated aqueous solution of succinic acid is known (see Patent Document 1).
The method in Patent Document 1, however, has a problem that, in the processes of separation and purification of succinic acid, there are too many steps because it requires an ordinary electrodialysis and the like prior to the step of the water-splitting electrodialysis in order to obtain the supersaturated aqueous solution. In addition, there is a problem, in the case of performing an industrial production by using the electrodialysis, that not only the initial investment cost for the purchase of equipments but also the running costs after the operation, such as use of a cleaning agent for an electrodialysis membrane, exchange of a deteriorated membrane and the like, are high.
As an alternative method, a process that involves the following steps is known; Ca(OH)2 is added to transform to Ca succinate, which is then recovered as crystals. Thereafter, calcium is precipitated as gypsum by adding sulfuric acid while succinic acid is recovered as a solution, and then succinic acid is crystallized by cooling (see Patent Document 2). However, the method of Patent Document 2 has a problem that there are too many steps and alkaline wastewater is produced at the time of recovering Ca succinate.
In addition, as an alternative method, a process that involves the following steps is known; ammonium sulfate is added under acidic condition, then succinic acid is recovered by salting-out. Thereafter, remaining ammonium sulfate is removed by extracting with methanol, and then the solvent is recovered to crystallize succinic acid (Patent Document 3). However, the method of Patent Document 3 has a problem that, because it involves treatments in the system of two liquid phases of water and methanol, not only the number of steps is increased, but also equipments durable for an organic solvent are needed.
For the reasons as mentioned above, it has been desired to establish the efficient production process that involves less steps, versatile equipments with low running costs, and simple steps of separation and purification.
[Patent Document 1] Japanese Patent No. 2944157
[Patent Document 2] Japanese Patent Laid-Open Publication No. S62-294090
[Patent Document 3] Japanese Patent Application Laid-Open No. 2001-514900